This invention relates to a heat exchanger of integral layered plate-fin type.
A heat exchanger of an integral layered plate-fin type as shown in FIGS. 1 and 2 is constructed by a plurality of flat hollow tubes 1 each of which is made by two metal plates 2 and 3, spacer-blocks 4 interposed between each pair of adjacent tubes 1 to form a layer of tubes, and heat conduction fins 5 disposed in respective spaces defined by the spacer-blocks 4 and the tubes 1 and these parts are assembled by integrally brazing them together. This type of heat exchanger has already been broadly used as a condenser for vapor compression air conditioning systems generaly used as an automobile cooler, a room cooler and the like.
This kind of heat exchanger is advantageous when it is used as an evaporator for air conditioning systems because its heat transfer efficiency is much higher than a usual fin-tube type heat exchanger. However, on the other hand, it is necessary to locate the evaporator A at an angle with with respect to the horizontal in a duct B as shown in FIG. 3, so that the dew derived from the air introduced by means of a fan D and formed on the outer surface of the evaporator may quickly drop into a drainpan C.
Considering the draining function and space of installation of the evaporator, it is preferable to set the tilting angle to about 45.degree.. But when the heat exchanger of integral layered plate-fin type is tilted, the refrigerant with two phases, i.e., gas and liquid phases, flowing through each tube as indicated by arrows in FIG. 2 is separated as shown in FIG. 4. Gaseous refrigerant gathers in the air inlet side (a) of each tube 1 and liquid refrigerant gathers in the air outlet side (b) as shown in FIG. 4, under the influence of gravity and of the difference between the specific gravities of the liquid and the gas. Such a flow condition decreases the heat transfer efficiency of the heat exchanger. More particularly, under the condition of gas-liquid distribution in tubes 1 as shown in FIG. 4, when the room temperature is high, the temperature difference between the air temperature and the temperature of the gaseous refrigerant at the air inlet side of the evaporator is smaller than the difference between the air temperature and the temperature of the liquid refrigerant, causing a lowered heat exchange efficiency. When the room temperature is relatively low, the evaporation pressure is decreased and the deviation of the liquid refrigerant in the air-outlet side (b) is increased, which cause the inconvenience of frosting in the air-outlet side (b).
Because of these problems, it has been considered difficult to adopt the heat exchanger of the integral layered plate-fin type as an evaporator.